The present invention relates generally to the field of inflatable devices for supporting the human body, and more particularly is concerned with a novel improved inflatable foot cushion to counter the force amplifications experienced by the foot, and particularly the heel area of the foot, when the body is in the supine position.
In the supine position, the foot assumes the shape of a wedge that tapers from the toes down to the heel. The mechanical force amplifications that are typically associated with a wedge are therefore also experienced by the wedge-shaped foot. The heel area, and more specifically the points of contact between the heel area and the substrate upon which the body is lying in the supine position, experiences mechanical force amplifications that are analogous to those experienced by the working edge of the typical wedge. In addition, when in the supine position, the lower legs function as levers with the heel areas serving as fulcrums, further amplifying the mechanical forces acting upon the heel areas.
The recognition that heel ulcers are caused by such mechanical forces (pressure, shear and frictional stresses) on the heel became clinically significant in the early 1980's. Since that time it has been found that offloading mechanical forces on the heel is the ideal way to prevent a pressure ulcer of the heel from developing (see NPUAP and EPUAP Guidelines). During the era of using pillows to offload mechanical forces on the heel, the occurrence of pressure ulcers of the heel continued to increase. Pressure ulcers of the heel are now running a close second to sacral pressure ulcers. When considering the deep tissue injury component of the pressure ulcer, pressure ulcers of the heel are now first in occurrence (see Vangilder, MacFarlane, Harrison, Lachenbruch and Meyer 254-261).
In 1994, a three-chambered Inflatable Foot Cushion was patented (U.S. Pat. No. 5,328,445). The prevention and treatment of pressure ulcers of the heel and other types of foot wounds have been exceptional when this patented inflatable foot cushion has been in use. The foot resting chamber of that device was constructed to resemble the keel of a boat. The objectives of the two main inflatable chambers of the patented Inflatable Foot Cushion that defined the foot resting chamber were the offloading the mechanical forces on the heel; the giving of symmetrical static air support to the calf, ankle and foot; and (3) the supporting of the sole of the foot to prevent foot drop and resultant injury. The third main chamber of that patented Inflatable Foot Cushion was an independent chamber (16) that was used beneath the two main chambers as an accessory chamber to elevate the inflatable foot cushion.